When drilling a wellbore, a drill string comprising a plurality of tubular members joined end to end may be fed through a wellbore. In certain circumstances, for example while drilling a deviated or horizontal wellbore, friction between the drill string and the wellbore may cause difficulty in inserting or removing the drill string from the wellbore. Friction reduction tools (FRT) or other hydraulically actuated tools may be used to generate friction reducing forces in the drill string to temporarily reduce friction between the drill string and the wellbore. Hydraulically actuated tools may be powered by pressure pulses of drilling fluid supplied through the drill string.
Typically, pressure pulses are generated using valves coupled to positive displacement motors to achieve desired pulse frequencies. However, positive displacement motors are subject to wear and vary in speed depending on the rate of fluid flow therethrough. Positive displacement motors are also affected by temperature, condition of rubber elements within the motors, and oil based fluid.